1. Field of the Invention
The invention relates to a method and a device for calibrating vectorial network analyzers for the measurement of linear and non-linear electrical parameters, preferably without through connections.
2. Discussion of the Background
In precision electronics, at low frequencies down towards microwave technology in the GHz range, vectorial network analyzers (VNA) are used for the accurate measurement of electronic parts and components of active and passive circuits and component groups.
A VNA registers the so-called scattering parameters of n-port devices (n=1, 2, . . . ), which are optionally converted into 2n-pole parameters (for example, Z-parameters or Y-parameters). However, with medium to high frequencies (fast circuits), these recorded data provide very large measurement errors. A so-called system-error correction of the VNA ensures that accurate measurements of fast electronic components are at all realisable. The measurement accuracy of VNAs depends primarily upon the availability of a method for system-error correction.
In the case of system-error correction, within the so-called calibration process, devices under test, which are known in part or in their entirety, are measured with regard to reflection and/or transmission behavior. This is known, for example, from DE 198 18 877 A1 and from DE 199 18 960 A1. Correction data (so-called error-values or coefficients) are obtained from these measured values, via special computational methods. With these correction data and a corresponding correction calculation, measured values, which have been freed from system errors of the VNA and supply lines (error couplings=crosstalk, error matching=reflections) are obtained for every required device under test.
The conventional form of description for the electrical behavior of components and circuits in high-frequency technology is provided via the scattering parameters (also referred to as S-parameters). The scattering parameters link together not currents and voltages, but wave sizes. This presentation is particularly well adapted to the physical circumstances of high-frequency technology. If required, these scattering parameters can be converted into other electrical network parameters, which link currents and voltages.
FIG. 1 shows a two-port device, which can be characterized by its scattering matrix [S]. Let the waves a1 and a2 be the waves flowing towards the two-port device, b1 and b2 corresponding to the waves propagated in the reverse direction. The following relationship applies:
      (                                        b            1                                                            b            2                                )    =            (                                                  S              11                                                          S              12                                                                          S              21                                                          S              22                                          )        ⁢          (                                                  a              1                                                                          a              2                                          )      
A linear component is adequately described by these S-parameters, which are indicated via the frequency. In the case of a component, which provides non-linear effects, with a supply of a signal with the frequency f0 at one port to the other ports, signals are generated with this fundamental frequency (f0) and other frequencies. These can be, for example, harmonics with the frequencies m*f0 (m=2, 3, 4, . . . ) or, in the case of a substitution of several transmission generators, inter-modulation products or mixing products. If one of the transmission generators is modulated, the number of frequencies is correspondingly large. The scattering parameters described above can also be advantageously used to describe the transmission behavior for these non-linear components. However, it must now be taken into consideration, that not only the ports, but also the frequencies are indicated.
Accordingly, the vectorial scattering parameters S2110 can be introduced as transmission parameters with the input port 1 in the case of the fundamental wave of frequency f0 and with the output port 2 in the case of the harmonic wave with the frequency f1=2*f0.
However, in many applications, these non-linear transmission properties of parts and components are not measured with a vectorial measuring device, because cost-favourable devices are not available. However, the vectorial values are extremely important for the modelling of parts such as transistors.
Purely scalar structures are the prior art for these measurements. Modern vectorial network analyzers provide software options, which permit the measurements of harmonics, inter-modulations, mixing products and similar in organizational terms. However, these are implemented in a purely scalar manner and accordingly without system-error correction.
Calibration methods, which require a large number of through connections are used for the measurement of linear multi-port devices. One frequently used method for the implementation of multi-port measurements is based upon the 10-term method according to DE 198 18 878 A1 and DE 199 18 697 A1. These require the connection of all test ports. That is to say, that even with an 8-port device, 28 through connections are required (calculated as follows: n/2*(n−1)).
8-port network analyzers are already conventional. The manufacturers often provides automatic calibration units for these devices. However, the internal cost for these applications is very high.
The user of modern measurement technology would like vectorial scattering parameters not only at the fundamental frequency but also with frequency translation at a reasonable cost. This cost should be disposed only slightly above the cost for current scattering-parameter measurements.